ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Physics => Topic started by: NE2000 on September 25, 2008, 10:15:02 am
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Just a thing I wanted to get my head over. We know that when electrical energy is being converted into heat and internal energy of the surrounding particles we consider it a transformation from a high-grade to a low-grade form of energy. However, when measuring the efficiency of energy conversion my bok has an electric heater as near 100% efficiency, which is fair enough considering the useful energy output is heat itself. But in the typical accompanying examples the only high-grade forms they talk about stuff being converted to is kinetic/electrical.
So my question is, when we refer to efficiency, if the objective of a converter is to convert electrical energy into low-grade forms of energy, then will it be considered efficient if that's what it does even though that energy is later 'lost' to surroundings? Additionally, would such converters be more efficient than those like motors which seek to convert electrical --> kinetic? Finally, when a light globe converts electrical --> light (let's ignore the heat) do we look at the light as a high-grade or low-grade form of energy because while my book says solar is high-grade it just seems like it can't be harnessed when it is coming out of a light globe.
Thanks.
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I have never heard of terms such as high-grade or low-grade energy, haha. It is not useful for unit 3/4 as far as I know, so this topic isn't really that important.
From Chemistry, efficiency measures how much energy is lost to the surroundings given the input, or rather, how much energy is not used for the purpose of the [whatever]. For that, electric motors are very efficient (go electromagnetism!), but combustion motors only run at about 25% efficiency. Batteries (galvanic cells) are very efficient (somewhere in the 90%), and fuel cells are lower down (about 60%), and burning fossil fuels for electricity generation has an overall efficiency of roughly 30%.
The key thing is how much of the input energy goes towards the [whatever]'s function. For an electric heater, its function is to heat water, and so a highly resistive coil is used which dissipates electric energy as heat. If tungsten wire (light globe) was used, despite some heat being emitted and more "high grade" energy being released, it is not efficient as the light energy does not serve the purpose of heating water. Similarly, using the heating element as a light globe isn't a good idea either.
I'm not exactly sure on how useful the terms "high" and "low" grade energy are... If it means how readily the energy can be harnessed, light is probably the worst, with solar cells operating at about 10% efficiency, and nature (photosynthesis) operating at about 1%.
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woah! we haven't even finished electricity yet and you're doing energy. that's why i'm dropping (physics) <<< gayyy
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I have never heard of terms such as high-grade or low-grade energy, haha. It is not useful for unit 3/4 as far as I know, so this topic isn't really that important.
From Chemistry, efficiency measures how much energy is lost to the surroundings given the input, or rather, how much energy is not used for the purpose of the [whatever]. For that, electric motors are very efficient (go electromagnetism!), but combustion motors only run at about 25% efficiency. Batteries (galvanic cells) are very efficient (somewhere in the 90%), and fuel cells are lower down (about 60%), and burning fossil fuels for electricity generation has an overall efficiency of roughly 30%.
The key thing is how much of the input energy goes towards the [whatever]'s function. For an electric heater, its function is to heat water, and so a highly resistive coil is used which dissipates electric energy as heat. If tungsten wire (light globe) was used, despite some heat being emitted and more "high grade" energy being released, it is not efficient as the light energy does not serve the purpose of heating water. Similarly, using the heating element as a light globe isn't a good idea either.
I'm not exactly sure on how useful the terms "high" and "low" grade energy are... If it means how readily the energy can be harnessed, light is probably the worst, with solar cells operating at about 10% efficiency, and nature (photosynthesis) operating at about 1%.
Thanks a lot; awesome explanation.
The high-grade and low-grade terms actually represent how easily the energy can be converted into other forms to suit our needs. My book said solar energy is high-grade pretty much because of PV cells. But for example electrical energy is high-grade because you can use it for so many appliances for so many different functions.